Buggy code:
@ SuppressWarnings ( "restriction" ) public class RootLayoutController { private static final String COMMAND_DELETE = "delete" ; private static final String COMMAND_DELETE_SHORTHAND = "del" ; private static final String COMMAND_SEARCH = "search" ; private static final String WHITESPACE = "<seq2seq4repair_space>" ; private static final String EMPTY_STRING = "" ; private static final String MESSAGE_LABEL_MODE_EDIT = "Edit<seq2seq4repair_space>mode" ; private static final String MESSAGE_LISTVIEW_EMPTY = "You<seq2seq4repair_space>have<seq2seq4repair_space>no<seq2seq4repair_space>task!" ; private static final String MESSAGE_FEEDBACK_ACTION_ADD = "Adding:" ; private static final String MESSAGE_FEEDBACK_ACTION_DELETE = "Deleting:" ; private static final String MESSAGE_FEEDBACK_TOTAL_TASK = "(%1$s<seq2seq4repair_space>tasks)" ; private static final String MESSAGE_FEEDBACK_ACTION_SEARCH = "Searching:" ; private static final String MESSAGE_ERROR_RESULT_DELETE = "Task<seq2seq4repair_space>-%1$s-<seq2seq4repair_space>not<seq2seq4repair_space>found." ; private static final KeyCombination HOTKEY_CTRL_TAB = new KeyCodeCombination ( KeyCode . TAB , KeyCombination . CONTROL_DOWN ) ; @ FXML private AnchorPane rootLayout ; @ FXML private TabPane tabPane ; @ FXML private Tab tabAll ; @ FXML private Tab tabToday ; @ FXML private Tab tabWeek ; @ FXML private JFXListView < String > listView ; @ FXML private TextField commandBar ; @ FXML private Label labelCurrentMode ; @ FXML private Label labelUserAction ; @ FXML private Label labelUserFeedback ; @ FXML private Label labelResult ; @ FXML private Button btnDel ; @ FXML private Button btnEdit ; @ FXML private Group groupUndoRedo ; @ FXML private Label labelUndoRedo ; @ FXML private Button btnUndoRedo ; private VirtualFlow < IndexedCell < String > > virtualFlow ; private IndexedCell < String > firstVisibleIndexedCell ; private IndexedCell < String > lastVisibleIndexedCell ; private Controller controller ; private ArrayList < Task > allTasks ; private ListProperty < String > listProperty ; private ObservableList < String > observableTaskList = FXCollections . observableArrayList ( ) ; private String inputFeedback ; private String userInput ; private String [ ] userInputArray ; private String userCommand ; private String userArguments ; private int previousSelectedTaskIndex ; private int previousCaretPosition ; private boolean isEditMode ; private boolean isExecuteCommand ; private boolean isUndo ; private boolean isRedo ; private boolean isUserRevertAction ; public void requestFocusForCommandBar ( ) { } public void selectFirstItemFromListView ( ) { } @ FXML private void initialize ( ) { } private void initTabSelectionListener ( ) { } private void initMouseListener ( ) { } private void initCommandBarListener ( ) { } private void initKeyboardListener ( ) { } private void populateListView ( ) { } private void refreshListView ( ) { } private void handleArrowKeys ( KeyEvent keyEvent ) { } @ SuppressWarnings ( "unchecked" ) private void initCustomViewportBehaviorForListView ( ) { } private void adjustViewportForListView ( ) { } private void handleFOneKey ( ) { } private void handleFTwoKey ( ) { } private void handleKeyStrokes ( ) { } private void handleEnterKey ( ) { } private void showUndoRedoButton ( ) { } private void handleDeleteKey ( ) { <START_BUG> controller . parseCommand ( ( ( ( RootLayoutController . COMMAND_DELETE ) + ( RootLayoutController . WHITESPACE ) ) + ( getSelectedTaskIndex ( ) ) ) , FLOATING_TAB ) ; <END_BUG> controller . executeCommand ( ) ; saveSelectedTaskIndex ( ) ; refreshListView ( ) ; restoreListViewPreviousSelection ( ) ; showUndoRedoButton ( ) ; } private void handleCtrlTab ( ) { } private void extractUserInput ( ) { } private void parseUserInput ( ) { } private void parseAdd ( ) { } private void parseDeleteImproved ( ) { } private void parseDelete ( ) { } private void parseSearch ( ) { } private void clearStoredUserInput ( ) { } private void clearFeedback ( ) { } private void showFeedback ( boolean isVisible ) { } private void showFeedback ( boolean isVisible , String userAction , String userFeedback ) { } private void showResult ( boolean isVisible , String resultString ) { } private void saveSelectedTaskIndex ( ) { } private void restoreListViewPreviousSelection ( ) { } private int getSelectedTaskIndex ( ) { } private String getSelectedTabName ( ) { } private void saveCaretPosition ( ) { } private void restoreCaretPosition ( ) { } private void moveCaretPositionToLast ( ) { } private int getCaretCurrentPosition ( ) { } public ArrayList < Task > getTaskList ( ) { } }

Fix:
controller . parseCommand ( ( ( ( RootLayoutController . COMMAND_DELETE ) + ( RootLayoutController . WHITESPACE ) ) + ( ( getSelectedTaskIndex ( ) ) + 1 ) ) , FLOATING_TAB ) ;